I'm making some ornamental exposed aggregate concrete blocks to match
those in our 80 year old garden wall.
I'm very pleased with my wooden mould - designed to make 10 blocks at
once.
So that it doesn't get wrecked by the water and concrete, and remains
reusable, I've varnished it with polyurethene, and lined it with blue
damp proof membrane.

Would polyurethene varnish on its own protect the wood?
The dpm plastic is a pain - it flaps about and makes it hard so see
where the screws are going when assembling the mould, and if it gets
creased, it shows in the blocks. It has the advantage though of
allowing easy release from the mould.

Any ideas on a better way to water-protect  the formwork?

Secondly, I think there is such a thing as a washer with teeth around
the edges, which I could nail over a screw hole so as to ensure that
the screw can only go in the correct place.
Anyone know what these things are called so I can tell the store what
I want to buy?

Thanks

tony

Sound like you're overdoing it. Commercially, a mould release agent is
used. A light smear of engine oil will do the job though.

Check out www.screwfix.com for builders metalwork.

dom@gglz.com coughed up some electrons that declared:

> 
> Sound like you're overdoing it. Commercially, a mould release agent is
> used. A light smear of engine oil will do the job though.
> 
> Check out www.screwfix.com for builders metalwork.

One of my (American) concreter's books suggest spraying on a mix of diesel
and sump oil. Not that I'm suggesting the OP do that, of course not...

Cheers

Tim

"tonyjeffs"  wrote in message 
news:e738f415-371a-4385-b2cb-117662969360@34g2000hsh.googlegroups.com...
> I'm making some ornamental exposed aggregate concrete blocks to match
> those in our 80 year old garden wall.
> I'm very pleased with my wooden mould - designed to make 10 blocks at
> once.
> So that it doesn't get wrecked by the water and concrete, and remains
> reusable, I've varnished it with polyurethene, and lined it with blue
> damp proof membrane.
>
> Would polyurethene varnish on its own protect the wood?
> The dpm plastic is a pain - it flaps about and makes it hard so see
> where the screws are going when assembling the mould, and if it gets
> creased, it shows in the blocks. It has the advantage though of
> allowing easy release from the mould.
>
> Any ideas on a better way to water-protect  the formwork?
>
> Secondly, I think there is such a thing as a washer with teeth around
> the edges, which I could nail over a screw hole so as to ensure that
> the screw can only go in the correct place.
> Anyone know what these things are called so I can tell the store what
> I want to buy?

Just brush ordinary diesel onto the wood before pouring the cement.

Silicon spray is a more expensive version producing the same result

On 18 Jul, 19:02, tonyjeffs  wrote:

> Any ideas on a better way to water-protect  the formwork?

I tend to use shellac, because it is easy to repair the worn surface
(shellac bonds well to old shellac). Varnish is strong but not so
sticky, so you can find it flaking off.

I also prefer wax (liquid emulsion of wax in wate, as sold to wood
turners) rather than oil. I've had one job where things came out with
an oily rainbow sheen and it didn't shift for years afterwards!

> Secondly, I think there is such a thing as a washer with teeth around
> the edges, which I could nail over a screw hole so as to ensure that
> the screw can only go in the correct place.

T nuts. They're intended to take an M6 screw or similar, but they also
work fine as a hammer-in hole reinforcer for dowel pins - they're
cheap enough too. You might even find that a machine screw is a better
choice than a woodscrew anyway.  If you're using MDF, then use a screw-
in threaded insert rather than a T nut.

Andy Dingley wrote:
> On 18 Jul, 19:02, tonyjeffs  wrote:
> 
>> Any ideas on a better way to water-protect  the formwork?
> 
> I tend to use shellac, because it is easy to repair the worn surface
> (shellac bonds well to old shellac). Varnish is strong but not so
> sticky, so you can find it flaking off.
> 
> I also prefer wax (liquid emulsion of wax in wate, as sold to wood
> turners) rather than oil. I've had one job where things came out with
> an oily rainbow sheen and it didn't shift for years afterwards!
> 
>> Secondly, I think there is such a thing as a washer with teeth around
>> the edges, which I could nail over a screw hole so as to ensure that
>> the screw can only go in the correct place.
> 
> T nuts. They're intended to take an M6 screw or similar, but they also
> work fine as a hammer-in hole reinforcer for dowel pins - they're
> cheap enough too. You might even find that a machine screw is a better
> choice than a woodscrew anyway.  If you're using MDF, then use a screw-
> in threaded insert rather than a T nut.

Vaseline, or anything from the mineral oil family e.g. paraffin wax. 
Good waterproofer and a good release agent

tonyjeffs wrote:
> I'm making some ornamental exposed aggregate concrete blocks to match
> those in our 80 year old garden wall.
> I'm very pleased with my wooden mould - designed to make 10 blocks at
> once.
> So that it doesn't get wrecked by the water and concrete, and remains
> reusable, I've varnished it with polyurethene, and lined it with blue
> damp proof membrane.
>
> Would polyurethene varnish on its own protect the wood?
> The dpm plastic is a pain - it flaps about and makes it hard so see
> where the screws are going when assembling the mould, and if it gets
> creased, it shows in the blocks. It has the advantage though of
> allowing easy release from the mould.
>
> Any ideas on a better way to water-protect  the formwork?
>
> Secondly, I think there is such a thing as a washer with teeth around
> the edges, which I could nail over a screw hole so as to ensure that
> the screw can only go in the correct place.
> Anyone know what these things are called so I can tell the store what
> I want to buy?
>
> Thanks
>
> tony

Tony

Have a look at:

http://www.pavingexpert.com/formwk01.htm
And the following excerpt is taken from there.  You could try googling for 
your nearest supply of Release Agent, Mould Oil or Shuttering Oil.

==============

Release Agents

All formwork, whether is be steel roadform or timber shuttering, needs to be 
coated with a Release Agent (Mould Oil) before any concrete is placed. The 
purpose of a Release Agent is to prevent the concrete bonding to the 
formwork and then 'scabbing' when the formwork is removed. They also help 
ensure the formwork stays clean and free from concrete, so that it can 
easily be re-used elsewhere.

There are many products on the market that can be used as Release Agents for 
formwork, but the most commonly used is known as 'Soap Oil'. This liquid is 
painted onto the formwork in advance of the concrete being poured and it 
dries, leaving behind a soapy or waxy residue that has no deleterious effect 
on the concrete. Where the finish of the concrete is not important, some 
contractors will save themselves a few bob by using engine oil or diesel in 
place of a proper release agent; while there is nothing technically wrong 
with this practice, it's not exactly environmentally friendly and should be 
avoided whenever possible.

Tanner-'op

Thanks everyone for all the info.
I'll try the diezel, or a proprietory mould release agent.
And get some T-nuts.

Knowing the terms alone helps!

Cheers

Tony

In message , Tanner-'op 
<tannerop@i.?.?.?.?.?.nvalid.com.invalid> writes
>
>http://www.pavingexpert.com/formwk01.htm

My Goodness!  Seeing that link reminded me of Cormaic, who has not 
posted for a long time.  Reading the site explains why :-(
-- 
Graeme

On Fri, 18 Jul 2008 18:25:21 -0700, tonyjeffs wrote:

> Thanks everyone for all the info.
> I'll try the diezel, or a proprietory mould release agent. And get some
> T-nuts.
> 
> Knowing the terms alone helps!
> 
> Cheers
> 
> Tony

==================================
I think you should go for the 'soap oil' option as the other suggested 
release agents (diesel etc.) might interfere with the mortar bonding when 
you come to build your wall.

Cic.

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